What are some 5.56 bolts that have tight headspace

That’s not how it works. The bolt’s dimensions create headspace within tolerances relative to your barrel/extension. Every bolt is slightly different, so that’s why Gucci end companies pair the bolt/barrel form factory.

Theoretically, a bolt that passes gauges on one barrel/extension could fail a different barrel, if that barrel’s tolerances were just outside the range. In general, higher end products will result in less chances of out of spec headspacing.

FWIW - A recent build of mind was DD barrel paired with an AO Precision (AO, not aero) and gave me suuuper tight headspace - still within spec but right on the line. Checked multiple AO bolts and received the same results. Wildly accurate upper.

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